Method, system, and article of manufacture for returning physical volumes

ABSTRACT

Provided are a method, system and article of manufacture for return processing in storage pools. A plurality of physical volumes are allocated to a first storage pool. A determination is made whether the first storage pool has more than a threshold number of empty physical volumes. If the first storage pool has more than the threshold number of empty physical volumes, then at least one empty physical volume is returned to a second storage pool.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 10/230,522filed on Aug. 29, 2002, which is incorporated herein by reference in itsentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method, system, and an article ofmanufacture for returning physical volumes.

2. Description of the Related Art

In prior art virtual tape storage systems, hard disk drive storageemulates tape drives and tape cartridges. For instance, host systemsperform input/output (I/O) operations with respect to a tape library byperforming I/O operations with respect to a set of hard disk drives thatemulate the tape library. In prior art virtual tape storage systems,such as the International Business Machines (IBM) Magstar** Virtual TapeServer, at least one virtual tape server (VTS) is coupled to a tapelibrary comprising numerous tape drives and tape cartridges. The VTS isalso coupled to a direct access storage device (DASD), comprised ofnumerous interconnected hard disk drives.**IBM, Tivoli, RS/6000, AIX, and Magstar, ESCON, OS/390 are trademarksof International Business Machines Corp.

The DASD functions as a cache to volumes in the tape library. In VTSoperations, the VTS processes the host's requests to access a volume inthe tape library and returns data for such requests, if possible, fromthe cache. If the volume is not in the cache, then the VTS recalls thevolume from the tape library to the cache, i.e., the VTS transfers datafrom the tape library to the cache. The VTS can respond to host requestsfor volumes that are present in the cache substantially faster thanrequests for volumes that have to be recalled from the tape library tothe cache. However, since the capacity of the cache is relatively smallwhen compared to the capacity of the tape library, not all volumes canbe kept in the cache. Hence, the VTS also premigrates volumes from thecache to the tape library, i.e., the VTS transfers data from the cacheto the tape cartridges in the tape library.

The tape library may comprise a plurality of storage pools. Each storagepool may comprise of zero, one or a plurality of tape cartridges.Requests from a host may identify a storage pool into which particulardata should be written into.

Notwithstanding the use of storage pools in a virtual tape library,there is a need in the art for improved techniques for managing storagepools in virtual tape library systems.

SUMMARY OF THE PREFERRED EMBODIMENTS

Provided are a method, system and article of manufacture for returnprocessing in storage pools. A plurality of physical volumes areallocated to a first storage pool. A determination is made whether thefirst storage pool has more than a threshold number of empty physicalvolumes. If the first storage pool has more than the threshold number ofempty physical volumes, then at least one empty physical volume isreturned to a second storage pool. In certain implementations, thereturned physical volume is the one that has undergone more usage thanother empty physical volumes present in the first storage pool.

In further implementations, the first storage pool is a data pool, thesecond storage pool is a scratch pool, the first storage pool is capableof borrowing additional physical volumes in the first storage pool fromthe second storage pool, and the threshold number is three.

Additional implementations provide a method, system, and article ofmanufacture for return processing in storage pools. A determination ismade whether a first storage pool has been updated within a firstelapsed time period. If the first storage pool has not been updatedwithin the first elapsed time period then a number of physical volumesto remain in the first storage pool is set to zero, the borrowing ofphysical volumes to the first storage pool from a second storage pool isdisabled, and the returning of physical volumes from the first storagepool is allowed.

In further implementations, normal returning and borrowing is allowed inthe first storage pool if the first storage pool been been updatedwithin a second elapsed time period, wherein the second elapsed timeperiod is less than the first elapsed time period.

In yet further implementations, a determination is made whether thefirst storage pool has been updated within a second elapsed time period,wherein the second elapsed time period is less than the first elapsedtime period. If the first storage pool has not been updated within thesecond elapsed time period the number of physical volumes to remain inthe first storage pool is set to three, the borrowing of physicalvolumes to the first storage pool from a second storage pool isdisabled, and the returning of physical volumes from the first storageis allowed.

The implementations achieve substantially uniform utilization of thephysical volumes by providing improved techniques for returning physicalvolumes to the scratch pool after the physical volumes have been usedand are empty. In certain implementations, at least three empty physicalvolumes that have been used the least are left in each storage pool.Certain implementations also reduce the unnecessary borrowing andreturning of physical volumes by limiting the borrow and returnprocesses to be used with recently active pools. Furthermore, when apool has been inactive for an extended period of time, empty physicalvolumes from the inactive pool may be returned to the scratch pool.Therefore, physical volumes are shared and reused more often by datapools and are used substantially uniformly.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings in which like reference numbers representcorresponding parts throughout:

FIG. 1 illustrates a block diagram of a computing environment, inaccordance with certain described aspects of the invention;

FIG. 2 illustrates a block diagram of physical volumes divided intopools, in accordance with certain described implementations of theinvention;

FIG. 3 illustrates a block diagram of pool data structures, inaccordance with certain described implementations of the invention;

FIG. 4 illustrates a block diagram of physical volume data structures,in accordance with certain described implementations of the invention;

FIG. 5 illustrates via a flow diagram and a corresponding table aprocess by which a physical volume spends entire life cycles in the samepool, in accordance with certain described implementations of theinvention;

FIG. 6 illustrates via a flow diagram and a corresponding table aprocess by which a physical volume is borrowed from a pool and thensubsequently returned to the original pool, in accordance with certaindescribed implementations of the invention;

FIG. 7 illustrates via a flow diagram and a corresponding table aprocess by which a physical tape volume is borrowed into a pool, used inthe pool, and then reused in the same pool, in accordance with certaindescribed implementations of the invention;

FIG. 8 illustrates logic for updating the active data timestamp in thepool data structure, in accordance with certain describedimplementations of the invention;

FIG. 9 illustrates logic for borrowing and returning physical volumesfor a pool, in accordance with certain described implementations of theinvention;

FIG. 10 illustrates logic for return processing of physical volumes, inaccordance with certain described implementations of the invention;

FIG. 11 illustrates logic for borrow processing of physical volumes, inaccordance with certain described implementations of the invention;

FIG. 12 illustrates a table that indicates borrowing policies that maybe applied to physical volumes, in accordance with certain describedimplementations of the invention;

FIG. 13 illustrates logic for borrow processing of physical volumesbased on certain borrowing policies, in accordance with certaindescribed implementations of the invention; and

FIG. 14 illustrates a block diagram of a computer architecture in whichcertain described aspects of the invention are implemented.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description, reference is made to the accompanyingdrawings which form a part hereof and which illustrate severalimplementations. It is understood that other implementations may beutilized and structural and operational changes may be made withoutdeparting from the scope of the present implementations.

FIG. 1 illustrates a computing environment utilizing a Virtual TapeServer (VTS) 100. Additional VTSs can be deployed, but for purposes ofillustration, a single VTS 100 is shown. The VTS 100 is any servercomputational device known in the art and includes any operating systemknown in the art. For instance, in certain implementations of theinvention, the VTS 100 may be implemented in one or more computerscomprising an IBM RS/6000** system and include the IBM AIX** operatingsystem.**IBM, Tivoli, RS/6000, AIX, and Magstar, ESCON, OS/390 are trademarksof International Business Machines Corp.

A plurality of hosts 102 a, 102 b, . . . , 102 n connect to the VTS 100.The hosts 102 a . . . 102 n may connect to the VTS 100 through a hostdata interface 103 channel, such as the Enterprise System Connection(ESCON)** channel or any other direct connection or switching mechanismknown in the art (e.g., fibre channel, Storage Area Network (SAN)interconnections, etc.). The hosts 102 a . . . 102 n may be anycomputational device known in the art, such as a personal computer, aworkstation, a server, a mainframe, a hand held computer, a palm topcomputer, a telephony device, network appliance, etc. The hosts 102 a .. . 102 n may include any operating system known in the art, such as theIBM OS/390** operating system.**IBM, Tivoli, RS/6000, AIX, and Magstar, ESCON, OS/390 are trademarksof International Business Machines Corp.

The VTS 100 includes at least one central processing unit (CPU) 104 andan application, such as a storage manager 105 that manages storage. Thestorage manager 105 may be implemented either as a standaloneapplication or as a part of one or more other applications. The storagemanager 105 manages a cache 106, such as a DASD file buffer, and aphysical library 108, such as a tape library. In certainimplementations, the storage manager 105 may include software to utilizea tape library, such as the IBM Magstar** Virtual Tape Server, and theIBM ADSTAR Distributed Management (ADSM) software or Tivoli** StorageManager. The storage manager 105 may perform or manage the data movementoperations between the hosts 102 a . . . 102 n, the cache 106, and thephysical library 108. Further details of the VTS technology aredescribed in the IBM publication “Magstar** Peer-to-Peer Virtual TapeServer Planning and Implementation Guide,” IBM document no. SG24-6115-00(Copyright IBM, 2000), which publication is incorporated herein byreference in its entirety.**IBM, Tivoli, RS/6000, AIX, and Magstar, ESCON, OS/390 are trademarksof International Business Machines Corp.

The physical library 108 may comprise an IBM Magstar Tape Library, suchas the Magstar** 3494 Tape Library, or any other tape library systemknown in the art. In certain implementations, the physical library 108comprises numerous physical devices 110 a, 110 b, . . . 110 n, such astape drives, CD ROM drives, DVD ROM drives, etc. The physical library108, in addition to including the physical devices 110 a . . . 110 n,includes physical volumes 114 a . . . 114 n. A physical volume may bemounted on any of the physical devices 110 a . . . 110 n. The physicalvolumes 114 a . . . 114 n may be of a variety of media types such astape cartridges, CD ROMs, DVDs, etc. In certain implementations thephysical volumes 114 a . . . 114 n may be mounted via mechanical loadingonto the physical devices 110 a . . . 110 n. The number of physicalvolumes 114 a . . . 114 n are larger than the number of physical devices110 a . . . 100 n.**IBM, Tivoli, RS/6000, AIX, and Magstar, ESCON, OS/390 are trademarksof International Business Machines Corp.

The cache 106 may comprise numerous interconnected hard disk drives. Thecache 106 improves performance by allowing host I/O requests from thehosts 102 a . . . 102 n to the physical library 108 to be serviced fromthe faster access cache 106 as opposed to the slower access physicallibrary 108. The disks in the cache may be arranged as a Direct AccessStorage Device (DASD), Just a Bunch of Disks (JBOD), Redundant Array ofInexpensive Disks (RAID), etc. The storage manager 105 maps the cache106 to a plurality of logical (virtual) devices (not shown). The hosts102 a . . . 102 n perform I/O operations by accessing logical (virtual)volumes 116 a . . . 116 n in the logical devices via the VTS 100. Thestorage manager 105 maps the logical volumes 116 a . . . 116 n to thephysical volumes 114 a . . . 114 n. Thus, the logical volumes 116 a . .. 1116 n in the cache 106 correspond to the physical volumes 114 a . . .114 n in the physical library 108. The logical volumes 116 a . . . 116 nresident on the cache 106 may change over time. The storage manager 105attempts to keep the more likely to be used logical volumes 116 a . . .116 n in the cache. Although the hosts 102 a . . . 102 n may access datavia the logical volumes, the data is physically stored in the physicalvolumes 114 a . . . 114 n mountable on the physical devices 110 a . . .110 n.

When a host 102 a . . . 102 n writes a logical volume to the VTS 100,the data is stored as a file in the cache 106. The cached data is latermigrated onto a physical volume 114 a . . . 114 n. The original logicalvolume is left in the cache 106 for cache hits. When the cache 106 fillsto a predetermined threshold, the logical volume data for a selectedlogical volume 116 a . . . 116 n is removed from the cache to free spacefor more logical volumes. In certain implementations, the storagemanager 105 removes from the cache 106 a selected logical volume(selected from the logical volumes 116 a . . . 116 n) that has beenresident on the cache 106 for the longest period of time.

When a host 102 a . . . 102 n requests a logical volume from the VTS100, a cache hit occurs if the logical volume is resident in the cache106. If the logical volume is not resident in the cache, then thestorage manager 105 determines whether the corresponding physical volume114 a . . . 114 n is mounted on one of the physical devices 110 a . . .10 n. If the corresponding physical volume 114 a . . . 114 n is notmounted then the storage manager 105 mounts the corresponding physicalvolume 114 a . . . 114 n on one of the physical devices 110 a . . . 110n. The data for the logical volume is then transferred back, i.e.,recalled, from the corresponding physical volume 114 a . . . 114 n.

Physical volumes 114 a . . . 114 n may be logically divided into one ormore storage pools (hereinafter referred to as pools) 120 a . . . 120 n,where each pool 120 a . . . 120 n has zero, one or more physical volumes114 a . . . 114 n. The hosts 102 a . . . 102 n may specify a particularpool 120 a . . . 120 n while reading and writing data via the VTS 100 byaccessing a logical volume 116 a . . . 116 n. In certainimplementations, each customer using the VTS 100 may have the customer'sdata stored on a separate pool 120 a . . . 120 n, thereby segregatingeach customer's data on a different subset of physical volumes 114 a . .. 114 n. The division of the physical volumes 114 a . . . 1114 n intopools 120 a . . . 120 n may be done for a variety of other reasons,including for storing different types of data in different pools, etc.

An application, such as, a library manager 122, is coupled to the VTS100 to manage the physical library 108 including the pools 120 a . . .120 n. In alternative implementations, the library manager 122 may becoupled to the physical library 108 or to any other computational device(not shown). The library manager 122 may either be a standaloneapplication or be part of any other application or subsystem, such as,the storage manager 105, the VTS 100, the physical library 108 etc. Thelibrary manager 122 may interact with various data structures such as aphysical volume data structure 124 and a pool data structure 126. Thephysical volume data structure 124 includes attributes of datastructures related to the physical volumes 114 a . . . 114 n, and thepool data structure 126 include attributes of data structures related tothe pools 120 a . . . 120 n. The physical volume data structure 124 andthe pool data structure 126 may be implemented in the VTS 100 in anymanner known in the art, such as via tables, linked lists, etc. Thelibrary manager 122 interacts with a library manager database 130, wherethe library manager database 130 may store information regarding thepools 120 a . . . 120 n and the physical volumes 114 a . . . 114 n. Incertain implementations, the library manager database 130 includesvarious instances of the physical volume data structure 124 and the pooldata structure 126. The library manager database 130 may be any databaseknown in the art such as a relational, hierarchical or object orienteddatabase management system. An application, such as a physical volumemonitor 132 may also be included in the VTS 100, where the physicalvolume monitor 132 may monitor the functioning of the physical volumes114 a . . . 114 n. A table or an equivalent data structure, such as aborrowing policy table 134 may also be included in the VTS 100. Theborrowing policy table 132 may contain rules for borrowing physicalvolumes 114 a . . . 114 n from one pool to another. In alternativeimplementations, the information contained in the borrowing policy table132 may be contained in other data structures, such as in the pool datastructure 126, and the borrowing policy table 132 may be absent. Inalternative implementations, the library manager database 130, thephysical volume data structure 124, the pool data structure 126, thephysical volume monitor 132, and the borrowing policy table 132 may becoupled to the physical library 108 or to any other computational device(not shown).

A customer input 136 for data from the VTS 100 may be conveyed to theVTS 100 via a host 102 a . . . 102 n (for illustration purposes thecustomer input 136 is shown coupled to host 102 n). The customer input136 many include requests for reading or writing data, where therequests are conveyed by the hosts 102 a . . . 102 n to the VTS 100. Inalternative implementations, the customer input 136 may be made directlyto the VTS 100 without involving the hosts 102 a . . . 102 n. Customerinput 136 may specify a pool 120 a . . . 120 n that is associated withthe data. In such a case the VTS 100 may satisfy the customer requestfrom the specified pool 120 a . . . 120 n. In certain alternativeimplementations, the VTS 100 or the library manager 122 may associate aspecific pool 120 a . . . 120 n with a specific customer input 136, evenwhen the specific customer input 136 does not specify any particularpool 120 a . . . 120 n.

Other alternative implementations of storage systems that do not conformto the illustrated computing environment may also be used forimplementations of the invention. For example, storage systems differentfrom a VTS may be used for alternative implementations of the invention.As long as storage pools 120 a . . . 120 n can be constructed from aplurality of physical volumes, implementations of the invention may beimplemented in a variety of computing environments.

FIG. 2 is a block diagram illustrating how physical volumes (such asphysical volumes 114 a . . . 114 n) may be divided into pools 120 a . .. 120 n, in accordance with certain implementations of the invention.While a specific example of dividing physical volumes 114 a . . . 114 ninto pools is shown, other variations in which the physical volumes 114a . . . 114 n are divided into pools 120 a . . . 120 n in a differentway are included within the scope of the implementations of theinvention.

The pool 120 a is also a scratch pool 120 a and may include a largenumber of physical volumes 114 a . . . 114 s selected from the physicalvolumes 114 a . . . 114 n. In certain implementations, the scratch pool120 a may include over a thousand physical volumes. The scratch pool 120a includes physical volumes of two different types,—type “J”(illustrated by reference numerals 114 a . . . 114 j) and type “K”(illustrated by reference numerals 114 k . . . 114 s). Type “J” and type“K” physical volumes have different characteristics. For example, onetype of physical volume may be capable of storing a larger amount ofdata when compared to the other type. However, access time for the typecapable of storing a larger amount of data may be slower when comparedto the access time of the other type. While only two types of physicalvolumes have been shown, the scratch pool 120 a may include a lesser ora greater number of types of physical volumes. The physical volumes 114a . . . 114 s included in the scratch pools 120 a have no active data,i.e., the physical volumes 114 a . . . 114 j are either empty, have datathat has expired, or contain data that may be overwritten by the hosts102 a . . . 102 n.

In certain implementations of the inventions, the plurality of pools 120b . . . 120 n may borrow and return physical volumes to the scratch pool120 a. The plurality of pools 120 b . . . 120 n may also be referred toas data pools or active pools as data may be written into physicalvolumes when physical volumes are present in pools 120 b . . . 120 n. InFIG. 2, pool 120 b has physical volumes of type J and type K, pool 120 chas physical volumes of type J only, and pool 120 n has physical volumesof type K only. A pool 120 b . . . 120 n may borrow a physical volumefrom the scratch pool 120 a when additional data needs to be writtenthat cannot be accommodated into the existing physical volumes withinthe pool 120 b . . . 120 n. When a physical volume is no longer requiredby a pool 120 b . . . 120 n, the physical volume may be returned to thescratch pool 120 a.

The scratch pool 120 a allows the sharing of a large number of physicalvolumes 114 a . . . 114 s, among the pools 120 b . . . 120 n. When apool 120 b . . . 120 n needs a physical volume for writing additionaldata, the new physical volume may be borrowed from the scratch pool 120a. A physical volume may be returned to the scratch pool 120 a after thephysical volume has been used by a pool 120 b . . . 120 n. In theabsence of the scratch pool 120 a, each pool 120 b . . . 120 n may needto be permanently assigned with a fixed set of physical volumes.

FIG. 3 illustrates a block diagram of the pool data structure 126, inaccordance with certain described implementations of the invention. Thepool data structure 126 may reside in the virtual tape server 100. Thepool data structure 126 is associated with each pool 120 a . . . 120 n,i.e., each pool 120 a . . . 120 n has an instance of the pool datastructure 126. In certain implementations, the instances of the pooldata structures 126 for each pool 120 a . . . 120 n may be constructedby the library manager 128 and stored in the library manager database130. In alternative implementations other processes in the VTS 100 mayconstruct the instances of the pool data structure 126 and store theinstances in locations different from the library manager database 130.

A first field of the pool data structure 126 is a “First media choicefor borrow” field 302. The entry of the field 302 for a particular poolindicates the preferred type of physical volume 114 a . . . 114 n thatthe particular pool may borrow from the scratch pool 120 a. In certainimplementations, the preferred type for the entry of field 302 may bechosen from (i) “none”, (ii) type “J”, (iii) type “K”, (iv) either oftype “J” or type “K”, where “J” and “K” are media types for differenttypes of physical volumes. If the “first media choice for borrow” field302 is “none” for a particular pool, then the particular pool is notallowed to borrow physical volumes of any type. Otherwise, the entry offield 302 reflects the type(s) of physical volumes that may be borrowedby a pool.

A second field of the pool data structure 126 is a “Second media choicefor borrow” field 304. The entry of field 304 for a particular poolindicates the second choice of the type of physical volume 114 a . . .114 n that the particular pool may borrow from the scratch pool 120 a.In certain implementations, the preferred type for the entry of field302 may be chosen from (i) neither of J or K, (ii) type J, (iii) type K,where J and K are media types for different types of physical volumes.

A third field of the pool data structure 126 is a “Return borrowedphysical volumes to scratch pool” field 306. If the field 306 is “yes”for a particular pool, then the particular pool may return a physicalvolume 114 a . . . 114 n to the scratch pool 120 a after the physicalvolume 114 a . . . 114 n is empty. If the field 206 is “no” for aparticular pool, then the particular pool may not return a physicalvolume to the scratch pool 120 a, i.e., the physical volume is apermanent member of the particular pool.

A fourth field of the pool data structure 126 is an “active datatimestamp” field 308. The field 308 for a particular pool includes thetime when data on the particular pool was accessed for any purpose,including in response to read or write requests from the hosts 102 a . .. 102 n. The “active data timestamp” field may be reset to zero.

FIG. 4 illustrates a block diagram of the physical volume data structure124, in accordance with certain implementations of the invention. Eachphysical volume 114 a . . . 114 n has an instance of the physical volumedata structure 124 coupled to the physical volume 114 a . . . 114 n. Incertain implementations, the instances of the physical volume datastructure for each physical volume 114 a . . . 114 n may be constructedby the library manager 128 and stored in the library manager database130. In alternative implementations other processes in the VTS 100 mayconstruct the instances of the physical volume data structure 126 andstore the instances in locations different from the library managerdatabase 130.

A first field of the physical volume data structure 124 is a“permanently assigned to a pool” field 402. If the “permanently assignedto a pool” field 402 for a particular physical volume indicates aspecific pool 120 a . . . 120 n, then the particular physical volume ispermanently assigned to the specific pool 120 a . . . 120 n. In certainimplementations, such permanent assignments may take place when theparticular physical volume is to be used exclusively by one user or aparticular application. The permanent assignment of a particularphysical volume to a storage pool 120 a . . . 120 n may be accomplishedusing an user interface associated with the library manager 128, duringthe time when the physical volumes 114 a . . . 114 n are first insertedinto the physical library 108.

If a particular physical volume is permanently assigned to a pool andthe pool is not a scratch pool, then the particular physical volume willat some point in time have data written into the particular physicalvolume. Even after all the data written to the particular physicalvolume has expired or has been removed, the physical volume still staysassigned to the pool.

A second field of the physical volume data structure 124 is a “currentpool” field 404 indicating the pool in which a physical volume 114 a . .. 114 n is currently present. For example, if the “current pool” fieldof a particular physical volume is pool 120 b, then the particularphysical volume is currently present in pool 120 b.

A third field of the physical volume data structure 124 is a “home pool”field 406 indicating the pool to which a specific physical volume 114 a. . . 114 n should be returned to whenever the specific physical volume114 a . . . 114 n is empty. In certain implementations of the invention,the home pool field 406 for a physical volume 114 a . . . 114 n is thescratch pool 120 a. For example, if the “home pool” field of aparticular physical volume is the scratch pool 120 a, then theparticular physical volume may be returned to the scratch pool 120 aafter the particular physical volume has been in some pool other thanthe scratch pool 120 a.

In certain implementations of the invention the “permanently assigned topool” field 402 is not used, and a physical volume is assumed to bepermanently assigned to the current pool of the physical volume if the“home pool” field 406 of the physical volume equals the “current pool”field 404 of the physical volume.

A fourth field of the physical volume data structure 124 is a “scratchcount” field 408 indicating the number of the times a physical volume114 a . . . 114 n has been borrowed and used. The value in the “scratchcount” field 408 for a particular physical volume is an indicator of thetotal number of times the particular physical volume has been used sincethe physical volume 114 a . . . 114 n was new. In alternativeimplementations the “scratch count” field 408 for a particular physicalvolume may reflect the number of times the particular physical volumewas returned.

A fifth field of the physical volume data structure 124 is an “empty oractive” field 410. If field 410 is labeled as “active” for a particularphysical volume then there is valid data on the particular physicalvolume and the physical volume is in use. If field 408 is labeled as“empty” for a particular physical volume then there is no valid data onthe particular physical volume and new data can be written on thephysical volume.

A sixth field of the physical volume data structure 124 is a “reservedby process” field 412. The field 412 may contain the identity of aprocess that has the physical volume associated with the physical volumedata structure 124 reserved for the process.

A seventh field of the physical volume data structure 124 is a “lockedby thread” field 414. The field 414 may contain the identity of a threadthat has the physical volume associated with the physical volume datastructure 124 locked by the thread. Such locking may be necessary whenthe physical volume associated with the physical volume data structure124 is being updated. There may also be other reasons for locking aphysical volume.

An eighth field of the physical volume data structure 124 is an “errorcondition” field 416. The field 416 may contain an error code thatreflects an error condition associated with the processing of thephysical volume corresponding to the physical volume data structure 124.

A ninth field of the physical volume data structure 124 is an “ejectprocessing flag” field. The field 418 may indicate that the physicalvolume corresponding to the physical volume data structure 124 is markedfor eject processing.

Alternative implementations of the invention may merge or not usecertain of the of the nine fields 402, 404, 406, 408, 410, 412, 414,416, 418, or use a subset of the nine fields 402, 404, 406, 408, 410,412, 414, 416, 418 in different storage devices.

FIG. 5 illustrates via a flow diagram 500 and a corresponding table 502,a process in which a physical volume spends the entire life cycle of thephysical volume in the same pool, in accordance with certainimplementations of the invention. Operations shown in the flow diagramof FIG. 5 may be performed by the library manager 122, or by any otherprocess coupled to the VTS 100.

The flow diagram 500 illustrates a pool N 504, where the pool N 504 maybe one pool out of the pools 120 a . . . 120 n. The pool N 504 has aphysical volume, where the physical volume has the name PV0001. Thecurrent pool 404 and the home pool 406 of the physical volume is alwayspool N. The “return borrowed physical volume to scratch pool” flag 306for the physical volume is permanently assigned to “no”. At step A 506the physical volume is empty. The various fields in the physical volumedata structure 124 of the physical volume and the pool data structure126 of the pool N 504 during the execution of step A 506 are shown inrow 502 a of table 502.

Subsequent to step A, data is written to the physical volume during thecourse of step B 508 and the physical volume becomes full, i.e., thereis no further space to write data into the physical volume. The variousfields in the physical volume data structure 124 and the pool datastructure 126 at the conclusion of step B 508 are shown in row 502 b oftable 502.

Subsequent to step B, the physical volume undergoes step C 510 andbecomes empty. In certain implementations, the physical volume undergoesstep C 510 when the data in the physical volume expires or is no longerrequired for some other reason. In alternative implementations, smallamounts of data remaining on the physical volume (an initial physicalvolume) can be transferred to another physical volume, emptying theinitial physical volume. The various fields in the physical volume datastructure 124 and the pool data structure 126 at the conclusion of stepC 508 are shown in row 502 c of table 502.

FIG. 5 illustrates the situation where a physical volume spends theentire life cycle of the physical volume in the same pool. Since thecurrent pool and home pools of the physical volume are pool N and pool Ndoes not return physical volumes, the physical volume spends the entirelife cycle of the physical volume in the same pool, i.e. in pool N 504.The physical volume alternates between empty and full state repeatedlyinside pool N 504.

FIG. 6 illustrates via a flow diagram 600 and a corresponding table 602,a process by which a physical volume is borrowed from a scratch pool andthen subsequently returned to the scratch pool, in accordance withcertain described implementations of the invention. Operations shown inthe flow diagram of FIG. 6 may be performed by the library manager 122,or by any other process coupled to the VTS 100.

The flow diagram 600 illustrates a pool M 604 and a pool N 606, wherethe pools M 604 and N 606 may be selected from the pools 120 a . . . 120n. A physical volume, where the physical volume has the name PV0002 maymove between pool M 604 and pool N 606. The home pool 606 of thephysical volume is always pool M 604. The “return borrowed physicalvolume to scratch pool” flag 306 for pool N 606 is permanently assignedto “Yes”.

At step A 608 the physical volume is empty and is present in pool M 604.The various fields in the physical volume data structure 124 for thephysical volume and the pool data structure 126 for pool N during step A608 are shown in row 602 a of table 602.

Subsequent to step A, during step B 610 the empty physical volume isborrowed by pool N 606 from pool M 604. The various fields in thephysical volume data structure 124 of the physical volume and the pooldata structure 126 of pool N 606 at the conclusion of step B 610 areshown in row 602 b of table 602. As a result of the movement of thephysical volume from pool M 604 to pool N 606 the “current pool” field404 of the physical volume changes to pool N in row 602 b (the currentpool 404 of the physical volume was pool M during step A, as shown inrow 602 a).

Subsequent to step B, during step C 612 the empty physical volume iswritten into in pool M and becomes full at the conclusion of step C 612.The various fields in the physical volume data structure 124 for thephysical volume and the pool data structure 126 for pool N at theconclusion of step C 612 are shown in row 602 c of table 602.

Subsequent to step C, during step D 614 the filled physical volume isemptied and at the conclusion of step D 614, the physical volume is inthe empty state in pool N 606. The various fields in the physical volumedata structure 124 for the physical volume and the pool data structure126 for pool N at the conclusion of step D 614 are shown in row 602 d oftable 602.

Subsequent to step D, during step E 616 the empty physical volume isreturned from pool N 606 to the “home pool” 406, i.e., the emptyphysical volume is returned to pool M 604. At the conclusion of step E616, the physical volume is in the empty state in pool M 604. Thevarious fields in the physical volume data structure 124 of the physicalvolume and the pool data structure 126 for pool N at the conclusion ofstep E 616 are shown in row 602 e of table 602. Since the home pool ofthe physical volume is pool M 604, and in pool N 606 the “returnborrowed physical volume to scratch pool” flag 306 for pool N 606 ispermanently assigned to “Yes”, the physical volume can be returned frompool N 606 to the home pool 406 (i.e., pool M 604).

In the VTS 100, the pool M 604 is the scratch pool 120 a. Therefore,FIG. 6 illustrates a process where a physical tape is borrowed from ascratch pool to a pool, used in the pool and returned back to thescratch pool when the pool is empty.

FIG. 7 illustrates via a flow diagram 700 and a corresponding table 702,a process by which a physical tape volume is borrowed into a pool, usedin the pool and then reused in the pool, in accordance with certaindescribed implementations of the invention. Operations shown in the flowdiagram of FIG. 7 may be performed by the library manager 122, or by anyother process coupled to the VTS 100.

The flow diagram 700 illustrates a pool M 704 and a pool N 706, wherethe pools M 704 and N 706 may be selected from the pools 120 a . . . 120n. A physical volume, where the physical volume has the name PV0003 maymove between pool M 604 and pool N 606. The home pool 706 of thephysical volume is always pool M 704. The “return borrowed physicalvolume to scratch pool” flag 306 for pool N 706 is permanently assignedto “No”.

At step A 708 the physical volume is empty and the physical volume ispresent in pool M 704. The various fields in the physical volume datastructure 124 for the physical volume and the pool data structure 126for pool N 706 during step A 708 are shown in row 702 a of table 702.

Subsequent to step A, during step B 710 the empty physical volume isborrowed by pool N 706 from pool M 704. The various fields in thephysical volume data structure 124 for the physical volume and the pooldata structure 126 for the pool N 706 at the conclusion of step B 710are shown in row 702 b of table 702. As a result of the movement of thephysical volume from pool M 704 to pool N 706, the “current pool” 404 ofthe physical volume changes to pool N in row 702 b (the current pool 404of the physical volume was pool M during step A 708, as shown in row 702a).

Subsequent to step B, during step C 712 the empty physical volume inpool M 704 is written into and the empty physical volume becomes full atthe conclusion of step C 712. The various fields in the physical volumedata structure 124 and the pool data structure 126 at the conclusion ofstep C 712 are shown in row 702 c of table 702.

Subsequent to step C, during step D 714 the filled physical volume isemptied and at the conclusion of step D 714, the physical volume is inthe empty state in pool N 706. The various fields in the physical volumedata structure 124 for the physical volume and the pool data structure126 for pool N 706 at the conclusion of step D 714 are shown in row 702d of table 602. The pool M 706 does not return the physical volume topool M 704 (or any other pool) because the “return borrowed physicalvolume to scratch pool” flag 306 for pool N 706 is permanently assignedto “No”. Hence, the empty physical volume is reused again and again inpool N 706.

In the VTS 100, the pool M 704 is the scratch pool 120 a. Therefore,FIG. 7 illustrates a process where a physical volume is borrowed from ascratch pool to a pool, and used and reused in the pool withoutreturning the physical volume to the scratch pool.

For managing storage pools borrow and return rules can be specified inmultiple physical volume pool systems and the rules may encompass theassignment of physical volume to the various pools. A scratch pool maybe maintained such that physical volumes may be shared among a pluralityof active pools. When an active pool does not have any availablephysical volume, the active pool may borrow a physical volume from thescratch pool. Subsequently, after the active pool has used the physicalvolume and does not need the physical volume any further, the activepool may return the physical volume to the scratch pool. Data can besegregated into different storage pools. In addition, mechanisms formanaging storage pools allow more efficient usage of physical volumes byallowing the sharing and reuse of physical volumes among a plurality ofactive pools.

Determining when to Borrow and Return Physical Volumes

An active pool is a pool that contains at least one physical volume thathas been modified, i.e., new data has been written in the physicalvolume or existing data in the physical volume has been removed. At anyinstant of time, some data pools 120 b . . . 120 n may be pools that arenot active. In certain implementations, the borrowing and returning ofphysical volumes are performed only by those data pools 120 b . . . 120n that are active pools.

FIG. 8 illustrates logic for updating the “active data timestamp” field308 in the pool data structure to facilitate the borrowing and returningof physical volumes, in accordance with certain describedimplementations of the invention. The logic may be performed by thephysical volume monitor 132, the library manager 122, the VTS 100, or byany other process coupled to the VTS 100, such as the storage manager105.

The process starts at block 802, where for each data pool 120 b . . .120 n during online processing the “active data timestamp” field 308 forthe pool data structure 126 is initialized to “zero.” During onlineprocessing, each data pool is processed such that appropriate physicalvolumes are borrowed and returned for each data pool.

Control proceeds to block 804, where the VTS 100 queues a file forpremigration to a selected pool 120 b . . . 120 n in the physicallibrary 108. Thus, the time of last update of data in the selected pool120 b . . . 120 n in the physical library 108 is the time at which theVTS 100 queues the file for premigration to the selected pool 120 b . .. 120 n. At block 806, the “active data timestamp” field 308 of the pooldata structure 126 corresponding to the selected pool 120 b . . . 120 nis updated with the time at which the VTS queued the file forpremigration. At the conclusion of block 806, the “active datatimestamp” field 308 for a selected pool 120 b . . . 120 n contains thetime at which data in the pool 120 b . . . 120 n was last updated.Control returns to block 804, and the logic of blocks 804 and 806 arerepeated as the VTS 100 keeps queuing additional files for premigration.

FIG. 9 illustrates logic for borrowing and returning physical volumesfor a pool, in accordance with certain described implementations of theinvention. The logic is performed by the physical volume monitor 132. Inalternative implementations, the logic may be performed by the librarymanager 122, the VTS 100, or by any other process coupled to the VTS100, such as the storage manager 105. The physical volume monitor 132processes each data pool 120 b . . . 120 n such that each data pool 120b . . . . 120 n returns and borrows physical volumes according to thelogic illustrated in FIG. 9.

The logic starts at block 900, where the physical volume monitor 132starts checking a selected data pool 120 b . . . 120 n for return andborrow processing. Control proceeds to block 902, where the physicalvolume monitor 132 determines if the “active data timestamp” field 308corresponding to the pool data structure 126 of the selected data pool120 b . . . 120 n is “zero”. If so, no change in data has taken place inthe selected data pool 120 b . . . 120 n since the last onlineprocessing (i.e., return and borrow processing). Therefore, no borrowingfrom the scratch pool 120 a or returning to the scratch pool 120 a isneeded. Control proceeds to block 904, where the physical volume monitor132 disables borrowing and returning for the selected data pool 120 b .. . 120 n and the process stops (at block 920) for the selected datapool 120 b . . . 120 n.

If at block 902, the physical volume monitor 132 determines that the“active data timestamp” field 308 corresponding to the pool datastructure 126 of the selected data pool 120 b . . . 120 n is not “zero”then control proceeds to block 906. At block 906, the physical volumemonitor 132 determines if the “active data timestamp” field 308 lags thecurrent time by more than a threshold time, N. In certainimplementations, N is set to “72 hours”, i.e., block 906 determines ifthe “active data timestamp” field 308 is more than 72 hours behind thecurrent time.

If at block 906, the “active data timestamp” field 308 lags the currenttime by greater than the threshold, N, then control proceeds to block908 where the physical volume monitor 132 sets the number of emptyphysical volumes to remain in the selected data pool 120 b . . . 120 nto zero, disables the borrowing of empty physical volumes for theselected data pool 120 b . . . 120 n, and enables the returning ofphysical volumes from the selected data pool 120 b . . . 120 n to thescratch pool 120 a. The rationale for these settings are as follows. Theselected data pool 120 b . . . 120 n has not been active for an extendedperiod of time N. The likelihood (when compared to other data pools) ofthe selected data pool needing an empty physical volume is low.Therefore, by restricting borrowing more physical volumes are freed upin the scratch pool 120 a. Returning is enabled because if data expiresin the selected data pool 120 b . . . 120 n, physical volumes should bereturned to the scratch pool 120 a. Since the likelihood of an update inthe selected data pool 120 b . . . 120 n is low, there is no need toretain any empty volumes in the selected data pool 120 b . . . 120 n.

Control proceeds to block 910 where the physical volume monitor 132determines if there is data in the selected data pool 120 b . . . 120 n.If so, control proceeds to block 920 where the process stops.

If at block 910, the physical volume monitor 132 determines that thereis no data in the selected data pool 120 b . . . 120 n then controlproceeds to block 912 where the physical volume monitor 132 resets the“active data timestamp” field 308 of the selected data pool 120 b . . .120 n to “zero”. The sequence of blocks 900, 902, 906, 908, 910 and 912may ensure the return of empty physical volumes in a selected data pool120 b . . . 120 n to the scratch pool 120 a and resets the “active datatimestamp” 308 of the selected data pool 120 b . . . 120 n to “zero”.

If at block 906, the physical volume monitor 132 determines that the“active data timestamp” 308 does not lag the current time by greaterthan the threshold, N, control proceeds to block 914. At block 914, thephysical volume monitor 132 determines if the “active data timestamp”field 308 lags the current time by a threshold, M, where M <=N. Incertain implementations, M may be 48 hours when N is 72 hours. If so,control proceeds to block 916 where the physical volume monitor 132 setsthe number of empty physical volumes to remain at three for the selecteddata pool 120 b . . . 120 n, disables borrowing for the selected datapool 120 b . . . 120 n and enables returning for the selected data pool120 b . . . 120 n. The rationale for these settings are as follows.Although the selected pool 120 b . . . 120 n has been active at sometime period between M and N (where M<=N), the selected pool 120 b . . .120 n has been inactive for at least the period M. Therefore, theselected data pool 120 b . . . 120 n has been inactive in the recentpast. Hence, by allowing up to three empty volumes to remain in theselected data pool 120 b . . . 120 n there is likely to be enough roomfor updates on the selected data pool and by restricting borrowing morephysical volumes are freed up in the scratch pool 120 a. Controlproceeds to block 920 where the process stops.

If at block 914, the physical volume monitor 132 determines that the“active data timestamp” field 308 does not lag the current time by athreshold, M, where M<=N, control proceeds to block 918, where theselected data pools 120 b . . . 120 n may perform normal return andborrow processing as described in FIGS. 2, 5, 6 and 7. At block 918, thephysical volume monitor 132 sets the number of empty physical volumes toremain to three for the selected pools 120 b . . . 120 n and enablesboth borrowing and returning for the selected pools 120 b . . . 120 n.The rationale for these settings are as follows. The selected data pool120 b . . . 120 n has been active recently. Therefore, by allowing up tothree empty volumes to remain in the selected data pool 120 b . . . 120n there is likely to be a large enough buffer of empty physical volumes114 a . . . 114 n for updates on the selected data pool and by enablingborrowing more physical volumes 114 a . . . 114 n can be borrowed fromthe scratch pool 120 a as needed. At the conclusion of 918, controlproceeds to block 920 where the process stops.

The implementations reduce the unnecessary borrowing and returning ofphysical volumes by adjusting the manner in which borrow and returnprocesses are used with data pools. When a data pool has been inactivefor an extended period of time, empty physical volumes from the inactivepool may be returned to the scratch pool and borrowing disabled for thedata pool. When a data pool has been active recently, up to threephysical volumes may be kept as a buffer for the data pool, and the datapool may borrow additional volumes from the scratch pool as needed. Whena data pool has not been active recently but has not been inactive foran extended period of time, borrowing may be disabled for the data poolbut the data pool may still be allowed to maintain a buffer of threeempty physical volumes. Therefore, there is a decreased demand for emptyphysical volumes on the scratch pool and physical volumes are shared andreused more often by data pools in the entire system.

Return Processing of Storage Pools

When physical volumes are reused, it may be better to reuse physicalvolumes uniformly, i.e., all physical volumes are used for approximatelythe same amount of time. By reusing each physical volume forapproximately the same amount of time, the possibility of errors in aparticular physical volume through overuse is reduced. Certainimplementations achieve substantially uniform utilization of thephysical volumes by providing improved techniques for returning physicalvolumes to the scratch pool 120 a after the physical volumes have beenused and are empty.

FIG. 10 illustrates logic for return processing of physical volumes, inaccordance with certain described implementations of the invention. Thelogic is performed by the physical volume monitor 132. In alternativeimplementations, the logic may be performed by the library manager 122,the VTS 100, or by any other process coupled to the VTS 100, such as thestorage manager 105. The physical volume monitor 132 processes each datapool 120 b . . . 120 n such that each data pool 120 b . . . . 120 nreturns physical volumes to the scratch pool 120 a according to thelogic illustrated in FIG. 10.

The logic starts at block 1000, with the physical volume monitor 132waiting for a message. While the physical volume monitor 132 may performadditional functions, a particular thread of the physical volume monitor132 may be dedicated towards waiting for the message that maypotentially trigger the returning of physical volumes 114 a . . . 114 n.Depending on the message, control may proceed to any of blocks 1002,1004 and 1006. At block 1002 the physical volume monitor 132 receives amessage that a certain fixed amount of time has elapsed. In certainimplementations, such a message may be received every hour. At block1004, the physical volume monitor 132 receives a message that asystemwide update (i.e., a reconcile on the VTS 100) has taken place. Asystemwide update involves reconciliation of all data in the VTS 100,the cache 106 and the physical library 108, such that the physicallibrary 108 possesses the latest updated copy of all data. At block1006, the physical volume monitor 132 receives a notification fromanother process that a particular physical volume has become empty.

From either of blocks 1002 or 1004 control proceeds to block 1008, wherea variable “POOL” representing an index into the data pools 120 b . . .120 n is assigned the integer “one”. The index indicates the selecteddata pool 120 b . . . 120 n that is under return processing by thephysical volume monitor 132. The total number of data pools 120 b . . .120 n is N and therefore a valid index into the data pools 120 b . . .120 n ranges from 1 to N.

Control proceeds to block 1010, where the physical volume monitor 132determines whether the variable “POOL” is greater than N, where N is thetotal number of data pools 120 b . . . 120 n. If so, control returns toblock 1000 because all data pools 120 b . . . 120 n have been processedfor return processing. Otherwise, control proceeds to block 1012 wherethe physical volume monitor 132 may determine if returning of physicalvolumes is enabled for the data pool being currently processed byexecuting the logic described in FIG. 9 in blocks 900-920. In theprocess described in blocks 900-920 certain data pools had returning ofphysical volumes disabled and certain data pools had returning ofphysical volumes enabled based on the “active data timestamp” field 308of the data pools. Furthermore, the process described in blocks 900-920also determined the number of empty physical volumes R to retain. Henceat block 1012, as part of determining whether returning of physicalvolumes is enabled for the data pool being currently processed thenumber of empty physical volumes to retain is also determined. If atblock 1012, it is determined that returning of physical volumes isenabled for the data pool being currently processed control proceeds toblock 1014. At block 1014, the physical volume monitor 132 may recordthe number of empty physical volumes R to retain in the pool beingcurrently processed (the number R was already determined while executingthe logic of block 1012 as part of the processing of blocks 900-920).

Control proceeds to block 1016 where for each data pool the physicalvolume monitor 132 creates a list of candidate physical volumes forreturn to the scratch pool 120 a. The candidate physical volumes areselected from the physical volumes 114 a . . . 114 n, where eachcandidate physical volume satisfies the following five conditions. Thefirst condition is that the “home pool” field 406 of a candidatephysical volume is the scratch pool 120 a (therefore, the candidatephysical volume can be returned to the scratch pool 120 a). The secondcondition is that the current pool of a candidate physical volume has“yes” for the “return borrowed physical volumes to scratch pool flag”field 306 (therefore, the current pool of the candidate physical volumeallows return of the candidate physical volume to the scratch pool 120a). The third condition is that there is no valid entry for the“reserved by process” field 412 of the physical volume data structure124 (therefore, the candidate physical volume is not reserved by anyparticular process). The fourth condition is that there is no validentry for the “error condition” field 416 of the physical volume datastructure 124 (therefore, there is no error condition associated withthe candidate physical volume). The fifth condition is that there is novalid entry for the “locked by thread” field 414 (therefore, thecandidate physical volume is not locked by any thread).

After the list of candidate physical volumes has been created in block1016, control proceeds to block 1018 where the candidate physicalvolumes are sorted based on the “scratch count” 408 of each physicalvolume. The “scratch count” field 408 indicates the number of the timesa physical volume 114 a . . . 114 n has been borrowed and used. Thevalue in the “scratch count” field 408 for a particular physical volumeis an indicator of the total number of times the particular physicalvolume has been used since the physical volume 114 a . . . 114 n wasnew. Therefore, the sorted list of candidate physical volumes reflectsthe relative frequency of prior usage of the candidate physical volumes.

Control proceeds to block 1020, where for each data pool 120 b . . . 120n the physical volume monitor 132 returns physical volumes from thesorted candidate physical volumes starting with the physical volume withthe highest scratch count until only R physical volumes remain in eachdata pool 120 b . . . 120 n. As determined in block 1014, R may be zeroor three depending on the number of physical volumes R to retain in thedata pool being processed. Note that the logic of blocks 900-920restricted R to be either zero or three. The physical volumes arereturned to the scratch pool 120 a.

Leaving three physical volumes in each data pool 120 b . . . 120 nensures that even if the storage manager 105 starts using an emptyphysical volume in a data pool 120 b . . . 120 n while the logic of FIG.10 is being executed, there would still be at least two empty physicalvolumes in each data pool 120 a . . . 120 n when the logic of FIG. 10has completed execution. Having at least three empty physical volumes ineach data pool ensures a buffer of physical volumes to reduce repeatedborrowing of physical volumes from the scratch pool 120 a. Inalternative implementations, the number of physical volumes left in eachdata pool 120 b . . . 120 n may be less than or greater than three. Instill further implementations, different data pools 120 b . . . 120 nmay have a different number of physical volumes left after thecompletion of the logic of block 1020. In certain situations where R iszero, no physical volume is left in the data pool being processed as thedata pool has been inactive too long.

At the conclusion of block 1020, control proceeds to block 1022 wherethe physical volume monitor 132 optionally increments the “scratchcount” field 408 of the physical volumes not returned to the scratchpool 120 a in block 1020. In alternative implementations, the “scratchcount” field 408 may be incremented elsewhere.

Control proceeds to block 1024, where the physical volume monitor 132increments the “POOL” variable so that the next pool from the data pool120 b . . . 120 n may be considered for return processing. Controlreturns to block 1010 where the next data pool 120 b . . . 120 n isconsidered for return processing.

If at block 1012, the physical volume monitor 132 determines that thereturning of data pools is disabled then control proceeds to block 1024.Also, at the conclusion of block 1006, control proceeds to block 1026where the particular physical volume that became empty in block 1006 isreturned to the scratch pool 120 a. At block 1016 only one physicalvolume is returned to the scratch pool 120 a. Control returns to block1000.

Return processing achieves substantially uniform utilization of thephysical volumes by providing improved techniques for returning physicalvolumes to the scratch pool 120 a after the physical volumes have beenused and are empty. In certain implementations of return processing, atleast three empty physical volumes that have been used the least areleft in each storage pool. Certain implementations of return processingalso reduce the unnecessary borrowing and returning of physical volumesby limiting the borrow and return processes to be used with recentlyactive pools. Furthermore, when a pool has been inactive for an extendedperiod of time, empty physical volumes from the inactive pool may bereturned to the scratch pool. Therefore, physical volumes are shared andreused more often by data pools and are used substantially uniformly.

Borrow Processing of Storage Pools

To ensure processing of information in a data storage pool 120 b . . .120 n, the data storage pool 120 b . . . 120 n may contain a reserve ofempty physical volumes. The physical volume monitor 132 may manage theborrowing of physical volumes 114 a . . . 114 n into the data storagepools 120 b . . . 120 n to help ensure that each data storage pool 120 b. . . 120 n has an adequate number of empty physical volumes. In certainimplementations, the empty physical volumes are borrowed from thescratch pool 120 a.

A small reserve of empty physical volumes in a data pool 120 b . . . 120n ensures that when additional updates to the data pool 120 b . . . 120n require additional storage space, such additional storage space isavailable on the empty physical volumes that have already been borrowedinto the data pool 120 b . . . 120 n. If such empty physical volumes hadnot already been borrowed, additional time may have to be spent toborrow empty physical volumes from the scratch pool 120 a when updatesare made to a data storage pool 120 b . . . 120 n. During borrowprocessing, the physical volume monitor 132 borrows an adequate numberof empty physical volumes 114 a . . . 114 n into data pools 120 b . . .120 n by anticipating the requirement for the empty physical volumes 114a . . . 114 n in the data storage pools 120 b . . . 120 n.

FIG. 11 illustrates logic for borrow processing of physical volumes, inaccordance with certain implementations of the invention. The logic isperformed by the physical volume monitor 132. In alternativeimplementations, the logic may be performed by the library manager 122,the VTS 100, or by any other process coupled to the VTS 100, such as thestorage manager 105. The physical volume monitor 132 processes each datapool 120 b . . . 120 n such that each data pool 120 b . . . . 120 nborrows physical volumes from the scratch pool 120 a according to thelogic illustrated in FIG. 11.

Processing starts at block 1100 with the physical volume monitor 132waiting for a message that may potentially trigger the borrowing ofphysical volumes 114 a . . . 114 n from the scratch pool 120 a. Whilethe physical volume monitor 132 may perform additional functions, aparticular thread of the physical volume monitor 132 may be dedicatedtowards waiting for the message that may potentially trigger theborrowing of physical volumes 114 a . . . 114 n. At block 1100, all datapools 120 b . . . 120 n are also marked as “unprocessed for borrowing”by the physical volume monitor 132.

At the completion of the logic described in block 1100, control mayproceed to either block 1102 or 1104. At block 1102 the physical volumemonitor 132 receives a message that indicates that a certain fixedamount of time has elapsed since the receipt of the last such message.In certain implementations, such a message may be received by thephysical volume monitor 132 every two minutes. At block 1104 thephysical volume monitor 132 receives a message that indicates that aread-write mount of a physical volume 114 a . . . 114 n has taken place.

From either of blocks 1102 or 1104 control proceeds to block 1106, wherea variable “POOL” representing an index into the data pools 120 b . . .120 n is assigned the integer “one”. The index indicates a selected datapool 120 b . . . 120 n that is under borrow processing by the physicalvolume monitor 132. The total number of data pools 120 b . . . 120 n isN and therefore a valid index into the data pools 120 b . . . 120 nranges from 1 to N.

Control proceeds to block 1108, where the physical volume monitor 132determines whether the variable “POOL” is greater than N, where N is thetotal number of data pools 120 b . . . 120 n. If so, control returns toblock 1100 because all data pools 120 b . . . 120 n have been processedfor return processing. Otherwise, control proceeds to block 1110, wherethe physical volume monitor 132 determines if borrowing is enabled forthe selected data pool (the logic of block 900-920 may have disabledcertain data pools 120 b . . . 120 n for borrowing). If borrowing is notenabled for the selected data pool then borrow processing should not beperformed for the selected data pool and control proceeds to block 1116where the variable “POOL” is incremented (i.e., the next data pool 120 b. . . 120 n is selected for potential borrow processing). Controlreturns to block 1108.

If at block 1110, the physical volume monitor 132 determines thatborrowing is enabled for the selected data pool then control proceeds toblock 1112 where the physical volume monitor 132 determines if theselected data pool has at least two empty physical volumes, for each ofwhich the following four conditions are satisfied. The first conditionis that the at least two empty physical volumes are read-write volumes,i.e., data can be read from the physical volumes and written into thephysical volumes. The second condition is that the “eject processingflag” field 418 of the physical volume data structure 124 is not markedfor eject processing (i.e., the at least two empty physical volumes arenot marked for eject processing). The third condition is that there isno valid entry for the “error condition” field 416 of the physicalvolume data structure 124 (therefore, there is no error conditionassociated with the at least two empty physical volumes). The fourthcondition is that there is no valid entry for the “locked by thread”field 414 (therefore, the at least two empty physical volumes are notlocked by any thread).

If at block 1112 it is determined that the data pool does not have leasttwo empty physical volumes that satisfy the four conditions controlproceeds to block 1114. At block 1114, the physical volume monitor 132borrows empty physical volumes as per certain borrowing rules (theborrowing rules will be described in FIGS. 12 and 13) into the selecteddata pool such that at the completion of block 1114 the data pool hastwo empty physical volumes. Further details of the borrowing techniquesused in block 1114 will be described in FIG. 13. Therefore, if the datapool does not have any empty physical volume that satisfy the fourconditions then the data pool borrows two empty physical volumes fromthe scratch pool 120 a. If the data pool has one empty physical volumethat satisfies the four conditions, then the data pool borrows one emptyphysical volume from the scratch pool 120 a. Control proceeds to block1116.

If at block 1112 the physical volume monitor 132 determines that thedata pool has at least two empty physical volumes then control proceedsto block 1116 because there is no need to borrow any additional emptyphysical volume to the data pool.

The logic of FIG. 11 ensures that each data pool 120 b . . . 120 n hasat least two empty physical volumes thereby ensuring that whenadditional updates to the data pool 120 b . . . 120 n require additionalstorage space such additional storage space is available on the at leasttwo empty physical volumes that have already been borrowed into the datapool 120 b . . . 120 n.

FIG. 12 illustrates details of the borrowing policy table 134 thatindicates borrowing policies that may be applied to borrow physicalvolumes 114 a . . . 114 n, in accordance with certain implementations ofthe invention. The borrowing policy table 134 contains rules that areused by the physical volume monitor 132 to determine which physicalvolumes 114 a . . . 114 n to borrow from a scratch pool 120 a into adata pool 120 b . . . 120 n.

In certain implementations there are two different types of physicalvolumes 114 a . . . 114 n. The two different types of physical volumesare of the “J” media type and the “K” media type. Physical volumes 114 a. . . 114 n that are borrowed from the scratch pool 120 a may beborrowed according to certain borrowing policies. The “first mediachoice for borrow” field 302 and the “second media choice for borrow”field 304 in the pool data structure 126 corresponding to a data pool120 b . . . 120 n may be used in association with the borrowing policytable 134 to determine what type of physical volume to borrow into adata pool 120 b . . . 120 n. The “first media choice for borrow” field302 and the “second media choice for borrow” field 304 can be set to oneof four values indicating the media type that the corresponding datapool may borrow. The four values are (1) “J” media type; (2) “K” mediatype; (3) “either media type”; and (4) “none”. The borrowing policytable illustrates six combinations 1202, 1204, 1206, 1208, 1210, 1212 ofthe settings of the “first media choice for borrow” field 302 and the“second media choice for borrow” field 304 that are meaningful. Theborrowing policy table 134 shows these six combinations 1202, 1204,1206, 1208, 1210, 1212 with entries for the “first media type to borrow”1214, the “second media type to borrow” 1216, the “interpretation” 1218and the and the “precedence for borrowing” 1220 corresponding to each ofthe six combinations 1202, 1204, 1206, 1208, 1210, 1212. In the“precedence for borrowing” 1216 entries with a lower numeric valueindicate a higher precedence for borrowing, i.e., “1” has the highestprecedence and “3” the lowest precedence. In the borrowing policy table132 the entries for the “first media type to borrow” 1214, the “secondmedia type to borrow” 1216, and the “interpretation” 1218 are shown tofacilitate the description of implementations and these entries may beomitted in the borrowing policy table 134 in the implementations.

As an example of the entries in the borrowing policy table 134, for theborrowing case “J-K” 1206 the “first media type to borrow” 1214 is “J”,the “second media type to borrow” 1216 is “K”. The “interpretation” 1218is that the second media type “K” is borrowed only when no media typesof the first media type “J” are available in the scratch pool 120 a. The“precedence of borrowing” 1220 is “2” for the borrowing case “J-K” 1206.

FIG. 13 illustrates logic for borrow processing of physical volumes 114a . . . 114 n based on the borrowing policy table 134, in accordancewith certain implementations of the invention; The logic is performed bythe physical volume monitor 132. In alternative implementations, thelogic may be performed by the library manager 122, the VTS 100, or byany other process coupled to the VTS 100, such as the storage manager105. The physical volume monitor 132 processes each data pool 120 b . .. 120 n such that each data pool 120 b . . . . 120 n returns physicalvolumes to the scratch pool 120 a according to the logic illustrated inFIG. 13.

Processing starts at block 1300 where the physical volume manager 132queries the storage manager 105 for the empty physical volumes on whichreads and writes can be performed in the data pools 120 b . . . 120 n.Control proceeds to block 1302 where the physical volume monitor 132counts the number of such empty physical volumes in each data pool 120 b. . . 120 n based on the response from the storage manager 105. Inalternative implementations, the physical volume monitor 132 maydetermine the number of empty physical volumes 132 on which reads andwrites can be performed without the assistance of the storage manager105.

Control proceeds to block 1304 where the physical volume monitor 132categorizes the data pools 120 b . . . 120 n that have less than twoempty physical volumes into one of the six borrowing cases 1202, 1204,1206, 1208, 1210, 1212 of the borrowing policy table 134. The physicalvolume monitor 132 performs the categorization of each data pool basedon the “first media choice for borrow” 302 field and the “second mediachoice for borrow” field 304 of the pool data structure 126corresponding to each data pool. For example, if for a data pool the“first media choice for borrow” 302 field is “J” and the “second mediachoice for borrow” filed 304 is “K” then the data pool is categorizedunder the borrowing case “J-K” 1206.

At the conclusion of the logic of block 1304, all data pools that haveless than two empty physical volumes are part of one of the sixborrowing cases 1202, 1204, 1206, 1208, 1210, 1212. For example,physical volumes 114 c, 114 d, 114 e, 114 g may all be categorized underthe borrowing case “K-J” 1208.

Control proceeds to block 1306 where the physical volume monitor 132begins processing the data pools categorized under the borrowing casewith the highest precedence. Control proceeds to block 1308, where afirst cycle is made through the data pools categorized under theborrowing case to select the data pools that have no empty physicalvolumes. For the data pools with no empty physical volumes, the physicalvolume monitor 132 borrows one physical volume 114 a . . . 114 n of anappropriate media type according to the borrowing rules laid down in theborrowing policy table 134 for the borrowing case of the data poolsbeing processed. If there is more than one physical volume of theappropriate media type that can be borrowed from the scratch pool 120 a,the physical volume with the lowest “scratch count” 408 is borrowed,i.e., while borrowing the least used physical volumes are borrowedthereby providing substantially uniform usage of all physical volumes.At the conclusion of block 1308, all data pools that started block 1308with no empty physical volume have one empty physical volume and alldata pools that started block 1308 with one empty physical volume hasone empty physical volume.

Control proceeds to block 1310, where in a second cycle through the datapools categorized under the borrowing case the physical volume monitor132 borrows one physical volume 114 a . . . 114 n of an appropriatemedia type according to the borrowing rules laid down in the borrowingpolicy table 134 for the borrowing case of the data pools beingprocessed that still need empty physical volumes. If there is more thanone physical volume of the appropriate media type that can be borrowedfrom the scratch pool 120 a, the physical volume with the lowest“scratch count” 408 is borrowed. The conclusion of block 1310 completesthe processing of data pools categorized for one borrowing case.

The advantage of borrowing empty physical volumes in two cycles is thatin the first cycle only data pools with no empty physical volumes borrowone empty physical volume. Only when each data pool has at least oneempty physical volume can the data pools attempt to borrow a secondphysical volume. Having two cycles is advantageous in situations wherethe scratch pool 120 a runs out of physical volumes of a particulartype.

Control proceeds to block 1312 where the physical volume monitor 132determines whether data pools corresponding to all borrowing cases havebeen processed. If not, control returns to block 1306, where thephysical volume monitor 132 begins processing the remaining unprocessedpools categorized under the borrowing case with the highest precedence.The loop formed by block 1306, 1308, 1310, 1312 may be executed sixtimes corresponding to the six borrowing cases 1202, 1204, 1206, 1208,1210, 1212.

If at block 1312, a determination is made that data pools correspondingto all borrowing cases 1202, 1204, 1206, 1208, 1210, 1212 have beenprocessed control proceeds to block 1314 where the physical volumemonitor 132 waits for a message to perform another round of borrowprocessing through all data pools 120 b . . . 120 n.

In certain implementations of the invention, during the execution of thelogic of FIG. 13 the scratch pool 120 a may run out physical volumes ofone media type. In such a case, borrowing is still performed for datapools that can borrow the other media type. Should the scratch pool 120a run out of both media types, borrow processing stops. The librarymanager 122 may be informed when the scratch pool 120 a runs out ofphysical volumes of a particular media type. The logic of FIG. 8 ensuresthat physical volumes are borrowed from the scratch pool 120 a accordingto the policies laid down in the borrowing policy table 134. An attemptis made to keep two empty physical volumes in data pool 120 b . . . 120n by appropriate borrowing strategies.

Borrow processing ensures a small reserve of empty physical volumes foreach data pool 120 b . . . 120 n. Physical volumes 114 a . . . 114 n areborrowed from the scratch pool 120 a when a data pool 120 b . . . 120 ndoes not have at least two empty physical volumes. While borrowing, theleast used physical volumes are borrowed from the scratch pool 120 athereby ensuring substantially uniform utilization of the data pools.Via the mechanisms of borrowing and returning the implementations of theinvention maintain neither too few nor too many empty physical volumesin each data pool. Also, the combination of borrowing precedence andsatisfying a first borrow for all pools followed by a second borrow forall pools ensures that a limited number of a specific media type isdistributed fairly among those pools that most require that media type.

Additional Implementation Details

The described techniques may be implemented as a method, apparatus orarticle of manufacture using standard programming and/or engineeringtechniques to produce software, firmware, hardware, or any combinationthereof. The term “article of manufacture” as used herein refers to codeor logic implemented in hardware logic (e.g., an integrated circuitchip, Programmable Gate Array (PGA), Application Specific IntegratedCircuit (ASIC), etc.) or a computer readable medium (e.g., magneticstorage medium, such as hard disk drives, floppy disks, tape), opticalstorage (e.g., CD-ROMs, optical disks, etc.), volatile and non-volatilememory devices (e.g., EEPROMs, ROMs, PROMs, RAMs, DRAMs, SRAMs,firmware, programmable logic, etc.). Code in the computer readablemedium is accessed and executed by a processor. The code in whichimplementations are made may further be accessible through atransmission media or from a file server over a network. In such cases,the article of manufacture in which the code is implemented may comprisea transmission media, such as a network transmission line, wirelesstransmission media, signals propagating through space, radio waves,infrared signals, etc. Of course, those skilled in the art willrecognize that many modifications may be made to this configurationwithout departing from the scope of the implementations, and that thearticle of manufacture may comprise any information bearing medium knownin the art.

FIG. 14 illustrates a block diagram of a computer architecture in whichcertain aspects of the invention are implemented. FIG. 14 illustratesone implementation of the VTS 100 and the hosts 102 a . . . 102 n. TheVTS 100 and the hosts 102 a . . . 102 n may implement a computerarchitecture 1400 having a processor 1402 (e.g., a microprocessor, suchas the CPU 104), a memory 1404 (e.g., a volatile memory device), andstorage 1406 (e.g., a non-volatile storage, magnetic disk drives,optical disk drives, tape drives, etc.). The storage 1406 may comprisean internal storage device, an attached storage device or a networkaccessible storage device. Programs in the storage 1406 may be loadedinto the memory 1404 and executed by the processor 1402 in a mannerknown in the art. The architecture may further include a network card1408 to enable communication with a network. The architecture may alsoinclude at least one input 1410, such as a keyboard, a touchscreen, apen, voice-activated input, etc., and at least one output 1412, such asa display device, a speaker, a printer, etc.

The logic of FIGS. 5-11 and 13 describe specific operations occurring ina particular order. Further, the operations may be performed in parallelas well as sequentially. In alternative implementations, certain of thelogic operations may be performed in a different order, modified orremoved and still implement implementations of the present invention.Morever, steps may be added to the above described logic and stillconform to the implementations. Yet further steps may be performed by asingle process or distributed processes.

While the hosts 102 a . . . 102 n and the VTS 100 communicate within aclient-server paradigm in the described implementations, the hosts 102 a. . . 102 n and the VTS 100 may also communicate within a peer-to-peeror any other paradigm known in the art. Furthermore, many of thesoftware and hardware components have been described in separate modulesfor purposes of illustration. Such components may be integrated into afewer number of components or divided into a larger number ofcomponents. Additionally, certain operations described as performed by aspecific component may be performed by other components.

While implementations of the invention have been described with ascratch pool, alternative implementations may be constructed whereactive pools may borrow and return physical volumes among the activepools (without involving a scratch pool) to reuse and share physicalvolumes. Alternative implementations may also be constructed with morethat one scratch pool. In alternative implementations, the functions ofa scratch pool may be performed by an active pool.

The data structures shown in FIGS. 3 and 4 show the data structures ashaving specific types of information. In alternative implementations,the physical volume data structure 124 and the pool data structure 126may have fewer, more or different fields than shown in the figures. Theborrowing policy table 134 may also be constructed differently and maycontain different information than shown in FIG. 12.

Certain groups of elements shown in the figures have been labeled withreference numerals having an identical numeric prefix followed by thesuffix “a”, the suffix “b”, or the suffix “n”. For example, the physicalvolumes are labeled 114 a, 114 b, . . . 114 n and the logical volumesare labeled 116 a, 116 b, . . . 116 n. Labeling groups of elements insuch a manner does not imply that different groups of elements containan identical number of elements in each group. For example, the numberof physical volumes 114 a . . . 114 n need not be the same as the numberof logical volumes 116 a . . . 116 n.

Therefore, the foregoing description of the implementations has beenpresented for the purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed. Many modifications and variations are possible in light ofthe above teaching. It is intended that the scope of the invention belimited not by this detailed description, but rather by the claimsappended hereto. The above specification, examples and data provide acomplete description of the manufacture and use of the composition ofthe invention. Since many implementations of the invention can be madewithout departing from the spirit and scope of the invention, theinvention resides in the claims hereinafter appended.

1. A method for return processing in storage pools, the methodcomprising: allocating a plurality of physical volumes to a firststorage pool; determining if the first storage pool has more than athreshold number of empty physical volumes; and if the first storagepool has more than the threshold number of empty physical volumes, thenreturning at least one empty physical volume to a second storage pool.2. The method of claim 1, wherein the returned at least one emptyphysical volume has undergone more usage than other empty physicalvolumes present in the first storage pool.
 3. The method of claim 1,further comprising: subsequent to allocating and prior to determining,receiving an indication that a systemwide update has taken place for thephysical volumes.
 4. The method of claim 1, further comprising:subsequent to allocating and prior to determining, receiving anindication that a fixed amount of time has elapsed since a previousattempt at returning at least one empty physical volume to a secondstorage pool.
 5. The method of claim 1, wherein the first storage poolis a data pool, wherein the second storage pool is a scratch pool,wherein the first storage pool is capable of borrowing additionalphysical volumes in the first storage pool from the second storage pool,and wherein the threshold number is three.
 6. A system for returnprocessing in storage pools, the system comprising: a first storagepool; a second storage pool; a plurality of physical volumes; means forallocating the plurality of physical volumes to the first storage pool;means for determining if the first storage pool has more than athreshold number of empty physical volumes; and means for returning atleast one empty physical volume to the second storage pool, if the firststorage pool has more than the threshold number of empty physicalvolumes.
 7. The system of claim 6, wherein the returned at least oneempty physical volume has undergone more usage than other empty physicalvolumes present in the first storage pool.
 8. The system of claim 6,further comprising: means for receiving an indication that a systemwideupdate has taken place for the physical volumes.
 9. The system of claim6, further comprising: means for receiving an indication that a fixedamount of time has elapsed since a previous attempt at returning atleast one empty physical volume to a second storage pool.
 10. The systemof claim 6, wherein the first storage pool is a data pool, wherein thesecond storage pool is a scratch pool, wherein the first storage pool iscapable of borrowing additional physical volumes in the first storagepool from the second storage pool, and wherein the threshold number isthree.
 11. An article of manufacture for return processing in storagepools, wherein the article of manufacture causes operations, theoperations comprising: allocating a plurality of physical volumes to afirst storage pool; determining if the first storage pool has more thana threshold number of empty physical volumes; and if the first storagepool has more than the threshold number of empty physical volumes, thenreturning at least one empty physical volume to a second storage pool.12. The article of manufacture of claim 11, wherein the returned atleast one empty physical volume has undergone more usage than otherempty physical volumes present in the first storage pool.
 13. Thearticle of manufacture of claim 11, the operations further comprising:subsequent to allocating and prior to determining, receiving anindication that a systemwide update has taken place for the physicalvolumes.
 14. The article of manufacture of claim 11, the operationsfurther comprising: subsequent to allocating and prior to determining,receiving an indication that a fixed amount of time has elapsed since aprevious attempt at returning at least one empty physical volume to asecond storage pool.
 15. The article of manufacture of claim 11, whereinthe first storage pool is a data pool, wherein the second storage poolis a scratch pool, wherein the first storage pool is capable ofborrowing additional physical volumes in the first storage pool from thesecond storage pool, and wherein the threshold number is three.